This invention relates to a coated glazing, a method of manufacture of said glazing and the use of an acidic gas to increase the haze (light scattering) exhibited by a coated glazing.
There is currently significant interest in devices such as photovoltaic (PV) modules, light emitting diodes (LEDs) and organic light emitting diodes (OLEDs). There is also considerable attention given to glass for horticulture. Manufacturers of these devices and glazings aim to manipulate light in a number of different ways.
Photovoltaic (PV) modules or solar cells are material junction devices which convert sunlight into direct current (DC) electrical power. When exposed to sunlight (consisting of energy from photons), the electric field of PV module p-n junctions separates pairs of free electrons and holes, thus generating a photo-voltage. A circuit from n-side to p-side allows the flow of electrons when the PV module is connected to an electrical load, while the area and other parameters of the PV module junction determine the available current. Electrical power is the product of the voltage times the current generated as the electrons and holes recombine.
It is to be understood that in the context of the present invention the term “PV module” includes any assembly of components generating the production of an electric current between its electrodes by conversion of solar radiation, whatever the dimensions of the assembly, the voltage and the intensity of the produced current, and whether or not this assembly of components presents one or more internal electrical connection(s) (in series and/or parallel). The term “PV module” within the meaning of the present invention is thus here equivalent to “photovoltaic device” or “photovoltaic panel”, as well as “photovoltaic cell”.
PV modules rely on substances known as semiconductors. Semiconductors are insulators in their pure form, but are able to conduct electricity when heated or combined with other materials. A semiconductor mixed, or “doped”, for example with phosphorous develops an excess of free electrons. This is known as an n-type semiconductor. A semiconductor doped with other materials, such as boron, develops an excess of “holes,” spaces that accept electrons. This is known as a p-type semiconductor.
A PV module joins n-type and p-type materials, with a layer in between known as a junction. Even in the absence of light, a small number of electrons move across the junction from the n-type to the p-type semiconductor, producing a small voltage. In the presence of light, photons dislodge a large number of electrons, which flow across the junction to create a current which can be used to power electrical devices.
Traditional PV modules use silicon in the n-type and p-type layers. The newest generation of thin-film PV module uses thin layers of cadmium telluride (CdTe), amorphous or microcrystalline silicon, or copper indium gallium deselenide (CIGS) instead.
The semiconductor junctions are formed in different ways, either as a p-i-n device in amorphous silicon (a-Si), or as a hetero-junction (e.g. with a thin cadmium sulphide layer that allows most sunlight to pass through) for CdTe and CIGS. In their simplest form, a-Si cells suffer from significant degradation in their power output (in the range 15-35%) when exposed to the sun. Better stability requires the use of thinner layers, however, this reduces light absorption and hence cell efficiency. This has led the industry to develop tandem and even triple layer devices that contain p-i-n cells stacked on top of each other.
Generally a transparent conductive oxide (TCO) layer forms the front electrical contact of the cell, and a metal layer forms the rear contact. The TCO may be based on doped zinc oxide (e.g. ZnO:Al [ZAO] or ZnO:B), tin oxide doped with fluorine (SnO2:F) or an oxide material of indium and tin (ITO). These materials are deposited chemically, such as for example by chemical vapour deposition (“CVD”), or physically, such as for example by vacuum deposition by magnetron sputtering.
For PV modules it can be advantageous to scatter the light that enters the module in order to improve its quantum efficiency. With respect to thin film silicon PV modules, it would be useful to increase the angle of scatter, and hence improve the trapping of weakly absorbed long wavelength light in the module.
LEDs are forward-biased p-n junction diodes made of semiconductor materials. A depletion region forms spontaneously across a p-n junction and prevents electrons and holes from recombining. When the p-n junction is forward-biased (switched on) with a sufficient voltage, the depletion region is narrowed and electrons can overcome the resistivity of the depletion region to cross the p-n junction into the p-type region where the recombination of electron-hole pairs causes the release of energy via the emission of light. This effect is called electroluminescence and the colour of the light is determined by the energy gap of the semiconductor. It is to be understood that in the context of the present invention the term “LED” includes any assembly of components that utilises a diode of semiconductor material that emits light when a forward bias is applied.
Early LED devices emitted low-intensity red light, but modern LEDs are available across the visible, ultraviolet and infra red wavelengths, with very high brightness. LEDs present many advantages over traditional light sources including lower energy consumption, longer lifetime, improved robustness, smaller size and faster switching. However, they are relatively expensive and require more precise current and heat management than traditional light sources. Applications of LEDs are diverse. They are used as low-energy indicators but also for replacements for traditional light sources in general lighting and automotive lighting. The compact size of LEDs has allowed new text and video displays and sensors to be developed, while their high switching rates are useful in communications technology.
OLEDs are LEDs in which the emissive electroluminescent layer(s) is a film of or based mainly on organic materials which emit light in response to an electric current. The organic molecules are electrically conductive as a result of delocalization of pi electrons caused by conjugation over all or part of the molecule. This layer of organic semiconductor material is situated between two electrodes in some cases. Generally, at least one of these electrodes is transparent. It is to be understood that in the context of the present invention the term “OLED” includes any assembly of components that utilises a diode of organic semiconductor material that emits light when a forward bias is applied. OLEDs can be used in television screens, computer monitors, small or portable system screens such as those found on mobile phones and the like.
A typical OLED comprises at least two organic layers, e.g. a conductive layer and an emissive layer, that are embedded between two electrodes. One electrode typically is made of a reflective metal. The other electrode typically is a transparent conductive coating (TCC) supported by a glass substrate. Indium tin oxide (ITO) is often used at the front portion of the OLED as the anode.
During operation, a voltage is applied across the OLED such that the anode is positive with respect to the cathode. A current of electrons flows through the device from cathode to anode and electrostatic forces bring the electrons and the holes towards each other and they recombine closer to the emissive layer resulting in the emission of radiation whose frequency is in the visible region.
LEDs and OLEDs are typically fabricated by providing a transparent conducting electrode comprising a transparent substrate and a conductive coating stack, and building successive layers thereon comprising the active region of the device and a further electrode—which may also be transparent. The transparent conducting electrode is frequently realised by depositing the conductive stack of coatings on the substrate using techniques such as CVD. The conductive stack typically comprises a TCC, such as a TCO, e.g. a doped metal oxide, as the uppermost layer (i.e. the furthest layer from the substrate). In addition to offering the requisite electrical properties and mechanical stability, the TCO should offer a suitable surface for deposition of further layers as the rest of the device is fabricated.
For LEDs and OLEDs the emphasis is clearly on extracting the light from the device such that it can serve its purpose rather than merely heating the device. Edge-lit LED luminaires, for instance, could benefit from light outcoupling (the escape of photons from an LED) by increasing light scattering. The extraction of light from OLED panels has hitherto generally been enhanced by the use of an external light extraction film e.g. on the external surface of a transparent substrate. It would be a significant breakthrough for OLED manufacture to provide an integrated substrate that combines an internal light extraction structure and a TCC.
Glazings for use in horticulture, e.g. in greenhouses, preferably transmit diffuse light and therefore glazings that can scatter light are of interest in this field.